1. Technical Field
The present invention relates to a multi-touch pad, especially related to a multi-touch pad having grid piezoresistor structure. The grid structure conducts current to flow more linearly from power end to ground end.
2. Description of Related Art
FIGS. 1˜3 show a prior art.
FIG. 1 shows a prior art multi-touch pad 14 which is disclosed in US20090256817. The multi-touch pad 14 is used by a user's finger to input instructions to a computer 12. A monitor 10 is electrically coupled to the computer 12 for displaying information. The multi-touch pad 14 has a top layer 18.
FIG. 2 shows a section view of the input device 14. Under the top cover 18, there is a stack of top electrode wires 14T, top resistor 15T, force sensing resistor 16, bottom resistor 15B, and bottom electrode wires 14B.
FIG. 3 shows a current pattern for the structure of FIG. 2.
FIG. 3 shows that a spot P is depressed as an example. Current 17 flows from a top wire 14T to a bottom wire 14B. Current 17 fans in, as shown in area 17T, to the spot P from the top wire 14T, and the current 17 fans out, as shown in area 17B, to the bottom wire 14B.
Since the resistance for the current fan in area and fan out area of the force sensing resistor at different pressed position equivalents to a resistance of a plurality of paralleled connected circuit path. The current is nonlinearity at different pressed position between the two electrodes. The current nonlinearity leads to a deviation of the pressed position calculation; the nearer the position is to the electrode, the larger the deviation is. For a touch pad structure, a current linearity is desirable so that the deviation of pressed position calculation can be reduced or eliminated.